This invention relates to inkjet printers and, more particularly, to an inkjet printer having a scanning printhead with a stationary ink supply.
Inkjet printers are well known. One common type of inkjet printer uses a replaceable print cartridge which contains a printhead and a supply of ink contained within the print cartridge. The print cartridge is not intended to be refillable and, when the initial supply of ink is depleted, the print cartridge is disposed of and a new print cartridge is installed within the scanning carriage. Frequent replacement of the print cartridge results in a relatively high operating cost.
The printhead has a useable life which is significantly longer than the time it takes to deplete the ink within the print cartridge. It is known to refill print cartridges intermittently by creating an opening through the print cartridge and manually refilling the print cartridge with ink. However, these refilling methods require manipulation by the user and are undesirable for various other reasons.
It is also known to provide an external, stationary ink reservoir, such as a flaccid bag containing ink, connected to the scanning print cartridge via a tube; however, these types of printing systems have various drawbacks including undesirable fluctuations in ink pressure in the print cartridge, an unreliable and complex fluid seal between the print cartridge and the external ink supply, increased printer size due to the external ink supply""s connection to the print cartridge, blockage in the ink delivery system, air accumulation in the tubes leading to the print cartridge, leakage of ink, high cost, and complexity. Such external ink supplies are referred to as off-axis ink supplies.
Most relevant to the present disclosure, Applicants have discovered that there is a diffusion mechanism that has the effect of growing bubbles and even pressurizing the ink delivery system. A bubble in the tubing has 100% relative humidity inside. Typically, the tube is in fluid communication with a flaccid bag containing ink. Thus, the pressure in the bubble is equalized with atmospheric pressure. In most environments, ambient humidity is less than 100%. Since the total pressure in the tube is the sum of the partial pressures, the partial pressure of air in the tube is less than the partial pressure of ambient air. As can be seen, this pressure difference decreases to zero as the ambient humidity approaches 100%. Thus, this pressure difference tends to be greatest in regions like Arizona and least for regions like Florida. As a result, rapid diffusion of air into the tube occurs, growing the bubble. In hot dry environments, some tubes (depending on their material, diameter, and thickness) can fill with air within a few days.
Excessive air in the tube will eventually be drawn into the printhead. Air in the printhead will render non-functional any pressure regulator internal to, or leading to, the print cartridge. For a non-pressurized ink supply system, excessive air delivered by the tubes will also cause printhead starvation.
What is needed is an improved inkjet printer, with a print cartridge and a separate ink delivery system connected to the print cartridge via one or more tubes, which avoids the air accumulation problems described above.
In the preferred embodiment, an inkjet printer includes a replaceable print cartridge which is inserted into a scanning carriage. An ink tube extends from the scanning carriage to a separate ink supply located within the printer. The external ink supply may be constantly pressurized, intermittently pressurized, or non-pressurized.
A separate valve between the tube(s) and the ink supply ensures that the pressure inside the tube will be substantially the same as ambient pressure. This minimizes water loss and air ingestion into the tube. This also prevents any expansion of air in the tube from reaching the ink supply. This valve is automatically actuated when it is detected that the printer is not being used.
If the print cartridge does not include a regulator valve, a second valve is inserted between the print cartridge and the tube so that the tube is sealed at its end by two valves when the printer is not being used.
Instead of a valve between the ink supply and the tube, the tube may be pressurized by a positive pressure source.